sighting vs landfall

sighting and landfall both are nouns.

Word	Noun	Adjective	Verb	Adverb
sighting	Yes	No	No	No
landfall	Yes	No	No	No

As nouns, landfall is a hyponym of sighting; that is, landfall is a word with a more specific, narrower meaning than sighting:

sighting: the act of observing
landfall: the first sighting of land from the sea after a voyage (or flight over water)

sighting (noun)	landfall (noun)
the act of observing	the first sighting of land from the sea after a voyage (or flight over water)
	the seacoast first sighted on a voyage (or flight over water)